Little change to Isaac, but intensification coming; Joyce forms

By: Dr. Jeff Masters , 3:13 PM GMT on August 23, 2012

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Tropical Storm Isaac is a large and impressive-looking storm on satellite images, but data from the Hurricane Hunters reveal that Isaac remains a minimal-strength tropical storm with 40 mph winds, as it heads westward across the Eastern Caribbean. An Air Force Reserve hurricane hunter aircraft which completed its mission into Isaac at 8 am EDT found top winds at the surface near 40 mph, and highest winds at their 5,000 foot flight level of 47 mph. A NOAA hurricane hunter aircraft flying at 10,000 feet has found top winds of 47 mph at that altitude. The Hurricane Hunters found a broad area of light winds with a central pressure of 1003 mb. The aircraft did not observe an eyewall trying to form, and recent microwave satellite images also show no signs of an eyewall forming. There does not appear to be much in the way of dry air near the core of Isaac, as seen on water vapor satellite loops, which is a big switch from what we've seen previously. Visible satellite loops show that Isaac has a much more symmetric circular cloud pattern, and has developed a Central Dense Overcast (CDO) of high cirrus clouds, the hallmark of an intensifying storm. These clouds have very cold cloud tops, indicating that the updrafts creating them are quite strong. An analysis of upper level winds from the University of Wisconsin CIMSS shows that an upper-level pattern of outflow supportive of significant strengthening has developed this morning, with an upper-level outflow channel now well-established to the north, and a new outflow channel opening to the south. Radar imagery from Puerto Rico shows some weak low-level spiral bands that are slowing intensifying and becoming more organized.


Figure 1. Morning radar image of Isaac taken from the Puerto Rico radar. Isaac's rain bands are weak, but are starting to take on a more spiraling shape.

Intensity forecast for Isaac
Isaac has consistently confounded predictions that it would intensify, but all the potential factors inhibiting intensification seem to have diminished to the point where intensification has to occur. Wind shear is low, 5 - 10 knots, and ocean temperatures are warm, 29°C, and these warm waters extend to great depth, giving the storm a high total heat content to work with. These factors, combined with the favorable upper-level outflow pattern and more symmetric cloud pattern, support intensification, and all of the intensity models except the HWRF model predict intensification of Isaac to a strong tropical storm or Category 1 hurricane by Friday afternoon. The latest 8 am EDT run of the SHIPS model predicts that wind shear will be light to moderate, 5 - 15 knots, for the next five days. The 11 am EDT wind probability forecast from NHC predicted a 34% chance that Isaac will become a hurricane by Friday afternoon, and a 6% chance it will be a Category 2 or stronger hurricane then. By Friday afternoon, Isaac will likely be close enough to Southwest Haiti that the inner core will be disrupted, and the storm will likely be a 45 - 55 mph tropical storm on Saturday and Sunday as it moves over Cuba. Once Isaac pops off the coast of Cuba into the Florida Straits, it will be over very warm waters of 31 - 32°C (88 - 90°F), wind shear will be light to moderate, and the upper-level wind pattern favorable for intensification, with low wind shear due to an upper-level anticyclone over the storm. It will probably take at least 24 hours with the storm's center over water for it to become a hurricane.

Impact of Isaac on the Islands
The south coast of Puerto Rico should see Isaac's heaviest rains and strongest winds beginning near 8 pm EDT tonight, with tropical storm-force winds of 40 - 45 mph potentially affecting the southwest portion of the island. The San Juan airport may be able to stay open during Isaac's passage, but with delays when spiral bands move overhead.

Heavy rains and tropical storm-force winds should arrive on the southern coast of the Dominican Republic late tonight, and the Santo Domingo airport will probably be closed on Friday. Rainfall amounts of 8 - 12 inches will likely affect the Dominican Republic Thursday through Saturday, creating dangerous flash floods and mudslides.

Isaac is potentially a very dangerous storm for Haiti, where 400,000 people still live outside underneath tarps in the wake of the 2010 earthquake. Heavy rains from Isaac will begin on Friday morning in Haiti, and last through Sunday. Rainfall amounts of 8 - 12 inches are possible, which will be capable of causing extreme flooding on the vegetation-denuded slopes of Haiti. It will be a major challenge to keep those Haitians living outside safe, if rainfall amounts of 5 - 10 inches occur.

Impact on Florida, Cuba, Jamaica, and the Bahamas
Florida, Cuba, Jamaica, and the Bahamas are all at risk of receiving flooding rains and high winds from Isaac. The latest set of 00Z (8 pm EDT) and 06Z (2 am EDT) model runs for Isaac are fairly unified for the coming three days, showing a west-northwestward track over Southwest Haiti and into Western Cuba. At the 4 - 5 day forecast period for Sunday and Monday, the models have come into better agreement, and have shifted west some. Our best-performing model, the ECMWF, has now shifted Isaac's path more to the east, but still is the westernmost of the models, predicting a landfall for Isaac near the Alabama/Florida border on Wednesday. While we do still have some models predicting a path up the east coast of Florida, model consensus now favors a path up the west coast of Florida through the Gulf of Mexico. The recent reformation of Isaac's center more to the south supports the idea that Isaac will take a track more to the west through the Gulf of Mexico. Since this now means a final landfall for Isaac in the Florida Panhandle is likely, the storm will probably have an extra day over water, increasing the odds that it will become a Category 2 or stronger hurricane before this final landfall. The NOAA jet is scheduled to fly into the storm this afternoon, to do a large-scale dropsonde mission to aid model forecasts. These missions can improve model forecasts by 10 - 20%, so the model runs that will be available early Friday morning should have increased reliability.

Impact on Tampa, Florida
The Republican National Convention begins on Monday in Tampa, Florida. The latest 11 am EDT wind probability forecast from NHC gives Tampa a 15% chance of receiving tropical storm-force winds and a 1% chance of receiving hurricane-force winds on Monday. The latest model tracks for Isaac suggests that the trough of low pressure pulling the storm to the north will not be strong enough to give Isaac a northeastward component of motion when it crosses Tampa's latitude. Thus, Isaac will have difficulty making a direct hit on Tampa without passing over a considerable amount of land first, making a multi-billion dollar hurricane disaster in Tampa very unlikely. I put the odds of a mass evacuation occurring during the convention at 1%; a limited evacuation of people in the Tampa Bay area living in mobile homes in low-lying areas is probably about 5 - 10 % likely. I have detailed information on Tampa's storm surge vulnerability in a post from last week.


Figure 2. Morning satellite image of Tropical Storm Joyce.

Tropical Storm Joyce forms in the Central Atlantic
The season's tenth named storm of the year, Tropical Storm Joyce, has formed in the Central Atlantic. Joyce's formation on August 23 puts 2012 in a tie for second place with 1995 for earliest formation date of the season's tenth storm. Only 2005 had an earlier appearance of the season's tenth storm, when Tropical Storm Jose formed at 2 pm EDT on August 22. None of the models show that Joyce will be a threat to the Lesser Antilles Islands, but it may be a storm that will affect Bermuda. It is possible that Joyce will complicate the track forecast for Isaac 4 - 5 days from now, when the storms may be close enough together to interact.

Jeff Masters

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1224. RJT185
Quoting MississippiWx:
The only explanation to all of this west business is that Isaac must be humping the ridge. Duh.


...the first real funny post in a while, thanks for the LOL.
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It seems like we all gave up and left...I wonder how Issac feels. Whoops...jumped da gun.
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Quoting presslord:
Why in the world would anyone listen to the NHC when we have easy access here to any number of anonymous, dysfunctional bloggers without any qualifications or credentials whatsoever?!?!?!?!


This is exactly why this is my sole source for information. I never bother looking anything up or historic data, since I get everything I need right here. It makes no difference to me that their short term 48 hr forecast has almost been spot on in the last two years. It is more important to know that the NHC is wrong the actual COC is further south and all the models are wrong.
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While everyone is wondering about the next computer runs, I am curious how much longer TS Isaac must go on its' westerly track before it becomes more of a GOM storm instead of a Florida storm.
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passing very close to this buoy

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1219. TXCWC
Quoting STXHurricanes2012:
Or the EURO playing like the GFS did against Debby when the GFS was the only one showing FL and the EURO showing TX! Could the other way around this time if the EURO is trying to do! LOL!!


So far trending last couple of days SEEMS TO INDICATE THAT as Euro has constantly been west of consensus and consensus gradually coming more west - as someone said yesterday - either way does not matter now as only way Isaac "gets out" is at the expense of someone - a more East path would be best case as less time to intensify
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I just have to say I find it hilarious that the ECMWF predicts a stronger ridge over florida when HPC shows a trough over southeastern U.S. in 5 days. No way does a system as strong as the ECMWF is depicting make it all the way to TX/LA border. Look at HPC forecast I find it very interesting

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the fact that NONE of the models predicted the long WSW motion Isaac did last night has me a lil worried... Let me see if I get this straight: NOW the GFS says Panama City Beach, EURO says LA COAST, AND the new GFDL also shifted WEST to Appolachicola??? hmmm... please correct me if i'm wrong, but I think Mobile, AL to Key West, FL is ALL gonna be affected by Isaac...
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Quoting MississippiWx:
The only explanation to all of this west business is that Isaac must be humping the ridge. Duh.

The places I can (but won't) go with this are astounding.
Member Since: August 3, 2008 Posts: 16 Comments: 5880
Quoting AtHomeInTX:
This can't be good.

little gustavish
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Quoting presslord:
he left because he told Jeff Masters to stick his website up his a**...and Jeff whacked him...and that's that...


He had and still has a lot of supporters and earned my respect. A real shame that all went down like that.
Live and learn.
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Quoting Levi32:
ECMWF certainly keeps the worry wide open for the Gulf of Mexico. I still think it looks unrealistically far west, but the eastern gulf coast has a lot of models pointed at it. I still want to see the 0z runs withe G-IV data in them.

You and me both. The models have been trending westward ever since Isaac developed, and it sure will be nice to have all that data and see if that bucks the trend or not.
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Quoting Chiggy:
12Z Euro at 168 hrs, 959mb, TX/LA border...!


Either the Euro will be hailed or flushed down the toilet. It sure is going out on a limb!
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1211. hercj
Quoting Levi32:


Hope came up with a general rule that if a tropical disturbance does not develop before it reaches the eastern Caribbean, it will not develop in the central-eastern Caribbean due to accelerating trade winds, but if it is going to develop, will wait to do so until the western Caribbean, or north of it.
Ok that seems to apply here doesn't it?
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The only explanation to all of this west business is that Isaac must be humping the ridge. Duh.
Member Since: July 15, 2006 Posts: 17 Comments: 10195
Quoting StormTracker2K:
What the hell is wrong withe Euro. I mean really from one of the best performing models to one of the worst in one year.



It actually has been doing the best with this storm so far...not sure how you say it's the worst??
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Quoting Chicklit:
There's a heck of a lotta decoupling going on!


?
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Quoting hurricanehanna:

I agree...not much liking these new model runs...


It's already had a history of foiling the majority of models. Good thing the ECMWF is on track. Even then, if this verifies, the ECMWF or "EURO" was too far east!

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1205. Jax82
Hot off the press taken just a bit ago. Today's Terra True Color image of Isaac!



Higher resolution image
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1204. Levi32
Quoting hercj:
Levi, have you ever heard of the Hope rule? Named after the late Dr John Hope. If so can you explain it to me.


Hope came up with a general rule that if a tropical disturbance does not develop before it reaches the eastern Caribbean, it will not develop in the central-eastern Caribbean due to accelerating trade winds, but if it is going to develop, will wait to do so until the western Caribbean, or north of it.
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I cannot buy into the 12z ECMWF at all given how persistent and strong ridging has proven itself to be over the Southern Plains, Texas, and Western Louisiana all summer long.
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1202. RJT185
Folks, please tone down the keyboard-based bravado.

Not only is it disheartening to see the attitudes, it is also rather annoying to have to sift through inane posts full of disdain just to find the few kernels of intelligent conversation.

Use the "-", "hide", and "ignore" features and move along!!


Hoping Isaac stays weak and disorganized and just ends up bringing rain to wherever it is needed most.
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Quoting Levi32:
ECMWF certainly keeps the worry wide open for the Gulf of Mexico. I still think it looks unrealistically far west, but the eastern gulf coast has a lot of models pointed at it. I still want to see the 0z runs withe G-IV data in them.


Me too.
Member Since: August 24, 2010 Posts: 0 Comments: 58
Quoting SouthDadeFish:
Honestly, with the hesitation in the intensification, I'm leaning towards a slightly more westward track. The only thing that I'm skeptical about for a west track, which may ending up being a huge thing, is that the frictional convergence over the Greater Antilles my try to slingshot this thing off to the N/NE then back WNW. I don't believe the global models have the resolution to predict that. I think the HWRF may, and that may be why it is farther east. Either scenario is plausible for now. I just don't think the G-IV flight data will help the models' interactions with the Greater Antilles.


I also expect a north jog island cross-over when he passes over Cuba that is going to freak out the S FL people for 12 hours before it resumes WNW.
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1199. TXCWC
Quoting AtHomeInTX:
This can't be good.



No it is not - that would be around a CAT 4 - Rita like path only a more intense version - 12Z GFS shifted west - now 12Z Euro shifts west - not good for Northern Gulf Coast - let's hope not a trend. As would mean odds of someone getting a very intense Cane goes up. I am still inclined for a Mobile to Pensacola landfall - BUT if models continue to trend west then all bets are off.
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There's a heck of a lotta decoupling going on!
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1197. CJ5
Quoting presslord:
it used to be that you could google "stick your website where the sun doesn't shine" and the whole story came up


LOL. I bet if you check google in a few minutes it will be back on top.
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Quoting LargoFl:
ty


Some logical thinking.
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1195. Grothar
Quoting Torgen:


Well, I'm certainly glad to hear that. I was wondering if I were in some alternate reality, because that just didn't sound like Grothar. I'm just checking in while working and can't keep a scorecard to stay up to date with all the drama, though. I just want to know when I need to start boarding up, if I do. It's going to take a half hour to kill all the brown recluses nesting in my hurricane panels.


Don't worry, Torgen. When I insult someone they know it. We are dealing with a possible devastating situation. Levi is a man not a boy. I can not speak for him, but I am sure it is not making him happy on either side. He has a lot of important work to do and does not need this diversion. Neither does the blog.

P.S. (I didn't mean to be condescending :) I knew you would catch on to what I was attempting.)

Now back to the weather.

Member Since: July 17, 2009 Posts: 71 Comments: 25972
Quoting StormTracker2K:


Jeff the Euro has this aimed at you this time.

It is about as far from me as Rita was in '05. So basically 40-50mph winds, a knocked over fence, and a few lawn chairs down.

Right now, in statistical terms, the Euro is an outlier in the long-range. It is showing a markedly different solution than most of the other major models (GFS, GFDL, HWRF), and is also rather different than most of the consensus models. I'm watching it to see how it shifts around, but so far, its kinda like the crazy kid standing away from the group screaming "pick me! pick me!".

I think it is feeling that Isaac will get stronger short term (which is why it tries to plow into Hispaniola), then get torn up by Hispaniola and Cuba. Then it stays weak-ish for a bit (for some odd reason) and eventually strengthens before landfall, when it catches another weakness.
Member Since: August 3, 2008 Posts: 16 Comments: 5880
Product: Air Force Vortex Message (URNT12 KNHC)
Transmitted: 23rd day of the month at 18:34Z
Aircraft: Air Force Aircraft (Last 3 digits of the tail number are 300)
Storm Number & Year: 09L in 2012
Storm Name: Isaac (flight in the North Atlantic basin)
Mission Number: 7
Observation Number: 09
A. Time of Center Fix: 23rd day of the month at 17:51:40Z
B. Center Fix Coordinates: 15°39'N 66°26'W (15.65N 66.4333W)
B. Center Fix Location: 193 miles (310 km) to the S (187°) from San Juan, Puerto Rico (USA).
C. Minimum Height at Standard Level: 1,459m (4,787ft) at 850mb
D. Estimated (by SFMR or visually) Maximum Surface Wind: 22kts (~ 25.3mph)
E. Location of the Estimated Maximum Surface Wind: 57 nautical miles (66 statute miles) to the NNW (335°) of center fix
F. Maximum Flight Level Wind Inbound: From 70° at 21kts (From the ENE at ~ 24.2mph)
G. Location of Maximum Flight Level Wind Inbound: 60 nautical miles (69 statute miles) to the NNW (332°) of center fix
H. Minimum Sea Level Pressure: 1004mb (29.65 inHg)
I. Maximum Flight Level Temp & Pressure Altitude Outside Eye: 19°C (66°F) at a pressure alt. of 1,525m (5,003ft)
J. Maximum Flight Level Temp & Pressure Altitude Inside Eye: 18°C (64°F) at a pressure alt. of 1,527m (5,010ft)
K. Dewpoint Temp (collected at same location as temp inside eye): 17°C (63°F)
K. Sea Surface Temp (collected at same location as temp inside eye): Not Available
L. Eye Character: Not Available
M. Eye Shape: Not Available
N. Fix Determined By: Penetration and Wind
N. Fix Level: 850mb
O. Navigation Fix Accuracy: 0.02 nautical miles
O. Meteorological Accuracy: 15 nautical miles



Vortex shows Isaac is cold core :)
Member Since: September 23, 2005 Posts: 14 Comments: 11037
Hi Everyone! Looks like I could be in for it here in Tallahassee. Do we feel pretty confident in the forecast since it's been relatively consistent the past few days? When should I call the ball on jumping ship if I need to?
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Quoting reedzone:
It doesn't make sense for a storm to smash right through a ridge... the weakness is over Florida and that is where Isaac is going to most likely head to. Whether it be the East Coast or West Coast. It's not passing 85W, in my opinion.


That is also stated by Accuweather.
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Quoting presslord:
These missions can improve model forecasts by 10 - 20%, so the model runs that will be available early Friday morning should have increased reliability.


Seems like there is an echo in the blog today. Lol.
Member Since: July 15, 2006 Posts: 17 Comments: 10195
1189. hercj
Quoting Levi32:
ECMWF certainly keeps the worry wide open for the Gulf of Mexico. I still think it looks unrealistically far west, but the eastern gulf coast has a lot of models pointed at it. I still want to see the 0z runs withe G-IV data in them.
Levi, have you ever heard of the Hope rule? Named after the late Dr John Hope. If so can you explain it to me.
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Well that looks familiar. Bummer

Member Since: August 24, 2010 Posts: 0 Comments: 58
Quoting hurricanealley:


What?




he said he wanted to go to lunch and grab a banana before going off to work
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Or the EURO playing like the GFS did against Debby when the GFS was the only one showing FL and the EURO showing TX! Could the other way around this time if the EURO is trying to do! LOL!!
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Quoting StormTracker2K:
Still south of the guidance but further north than the 0Z run.



Yup
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Actually that area the euro has hitting is good for me at least. I have a lot of clients there that i do work for
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Dvorak Fixes Storm History
DATE TIME LAT LON CLASSIFICATION ID NAME
20120823 1745 15.9 66.3 T3.0/3.0 09L ISAAC
20120823 1145 15.0 65.2 T3.0/3.0 09L ISAAC
20120823 0545 14.2 64.5 T3.0/3.0 09L ISAAC
20120822 2345 15.6 62.0 T3.0/3.0 09L ISAAC

Microwave Fixes Storm History
DATE TIME BASIN LAT LON SENSOR ID NAME
20120822 1214 ATL 16.0 58.3 SSMIS 09L ISAAC
20120822 0919 ATL 15.9 57.4 SSMIS 09L ISAAC
20120821 1311 ATL 14.8 52.1 AMSU 09L NONAME
20120819 0820 ATL 14.5 35.5 SSMIS 94L 94L
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What is the chance that Tallahassee could get hit with TS winds and heavy rain? Also is it likely schools will be closed next week?
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These missions can improve model forecasts by 10 - 20%, so the model runs that will be available early Friday morning should have increased reliability.
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Levi i see the ridge building back in and stalling Isaac on the last gfs run do you think it will hapen that the rige will block isaac eventually
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Quoting AtHomeInTX:
This can't be good.



Wow. This Isaac has more time in the gulf now according to the top ranked EURO.
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Quoting AtHomeInTX:
This can't be good.


I agree...not much liking these new model runs...
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Quoting reedzone:
EURO is out to lunch this afternoon. A Hurricane cannot slam into a ridge, maybe a banana like ridge, but not the side of a ridge.. Should recurve near Florida. I'm holding off on the REED run until I see better data in the models tonight. Off to work.


We will all wait in enthusiastic anticipation.
Member Since: July 15, 2006 Posts: 17 Comments: 10195
Quoting TXHuRRicanE:
just got back.... WHERE IS THE CENTER


ummm I'd leave again
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1174. Levi32
ECMWF certainly keeps the worry wide open for the Gulf of Mexico. I still think it looks unrealistically far west, but the eastern gulf coast has a lot of models pointed at it. I still want to see the 0z runs withe G-IV data in them.
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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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